1. Field of the Invention
The present disclosure relates to an organic light emitting diode display device, and more particularly, to an organic light emitting diode display device where the emission efficiency and the viewing angle are improved.
2. Discussion of the Related Art
Recently, various flat panel displays (FPDs) such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, organic light emitting diode (OLED) display devices and field emission display (FED) devices have been widely researched and used.
Among various FPDs, since the OLED display device of an emissive device does not require an additional light source such as a backlight unit for the LCD device, the OLED display device has a light weight and a thin profile. As compared with the LCD device, the OLED display device has superior properties in a viewing angle, a contrast ratio and a power consumption. In addition, the OLED display device can be driven by a direct current (DC) low voltage and has a high response speed. Since internal components of the OLED display device are solid, the OLED display device is resistant to external shocks and has a wide available temperature range. Specifically, since the manufacturing process for the OLED display device is simple, a production cost for the OLED display device can be reduced as compared with the LCD device.
FIG. 1 is a plan view showing an organic light emitting diode display device according to the related art, and FIG. 2 is a cross-sectional view taken along a line II-II of FIG. 1.
In FIG. 1, an organic light emitting diode (OLED) display device 10 according to the related art includes a substrate 11 having a pixel region PA and a driving region DA below the pixel region PA, a first electrode 15 in the pixel region PA on the substrate 11, an auxiliary electrode 14 in the driving region DA on the substrate 11 and a bank layer 17 surrounding the pixel region PA and the driving region DA. The pixel region PA includes first to third sub-pixels SP1 to SP3. The first, second and third sub-pixels SP1, SP2 and SP3 display red, green and blue colors, respectively, and constitute a unit pixel.
Although not shown, a driving unit for driving the first to third sub-pixels SP1 to SP3 is formed in the driving region DA. The driving unit includes at least one thin film transistor (TFT) and is formed under the auxiliary electrode 14 to be connected to the first electrode 15.
In FIG. 2, the first electrode 15 is formed in the pixel region PA on the substrate 11, and the auxiliary electrode 14 is formed in the driving region DA on the substrate 11 to be spaced apart from the first electrode 15.
The bank layer 17 is formed on the auxiliary electrode 14 and the first electrode 15 to cover an edge portion of the first electrode 15 and has an opening 40 to expose the auxiliary electrode 14.
An organic layer 20 is formed on the first electrode 15, and a second electrode 25 is formed on the organic layer 20. The second electrode 25 is formed on the entire surface of the substrate 11 having the organic layer 20 and is connected to the auxiliary electrode 14 through the opening 40. Here, the first and second electrodes 15 and 25 and the organic layer between the first and second electrodes 15 and 25 constitute a light emitting diode E.
FIG. 3 is a cross-sectional view showing first to third sub-pixels of a pixel region of an organic light emitting diode display device according to the related art. In FIG. 3, each of first to third sub-pixels SP1 to SP3 of an organic light emitting diode (OLED) display device 10 according to the related art includes first and second electrodes 15 and 25 facing each other and an organic layer 20 disposed between the first and second electrodes 15 and 25.
The organic layer 20 includes a hole injecting layer HIL on the first electrode 15, a hole transporting layer HTL on the hole injecting layer HIL, one of red, green and blue emitting material layers EML(R), EML(G) and EML(B) on the hole transporting layer HTL, an electron transporting layer ETL on the one of red, green and blue emitting material layers EML(R), EML(G) and EML(B).
The first electrode 15 as a reflective electrode has a triple-layered structure including two transparent conductive material layers ITO and a reflective layer REF between the two transparent conductive material layers ITO. The second electrode 25 as a transflective electrode transmits a portion of a light generated by the organic layer 20 and reflects the other portion of the light generated by the organic layer 20.
The light reflected by the second electrode 25 is reflected again by the first electrode 15, and when the lights reflected by the first and second electrodes 15 and 25 have the same wavelength as each other, they give rise to constructive interference called a microcavity. As a result, a luminance property and an emission efficiency of the OLED display device 10 are improved.
To generate such a microcavity, the organic layer 20 may have different thicknesses in the first to third sub-pixels SP1 to SP3 based on an optical distance that can generate the microcavity. For example, the hole injecting layer HIL or the hole transporting layer HTL under the red, green and blue emitting material layers EML(R), EML(G) and EML(B) may be sequentially reduced.
At this time, the hole injecting layer HIL or the hole transporting layer HTL is formed of a relatively thick thickness to satisfy the optical distance for the microcavity. Accordingly, a problem occurs that the emission efficiency is reduced with an increase in the thickness of the hole injecting layer HIL or the hole transporting layer HTL.
In addition, although a luminance along a front direction is improved, a luminance viewing angle and a chrominance property are deteriorated as the conventional organic light emitting diode display device has a microcavity structure.
Meanwhile, the luminance viewing angle and the chrominance property may be improved by placing a color filter layer on the light emitting diode E. However, since the number of fabrication steps and the material cost increase due to the color filter layer, there is a problem that the manufacturing cost increases.